Proton exchange membrane (PEM) fuel cells are one of the most important types of fuel cells due to their ability to work at low temperature, and their low weight and volume. This has made PEM fuel cells a competitive alternative power source in stationary and automotive applications. However, the extensive use of PEM fuel cell depends on its reliability and cost efficiency. Over the years, the fuel cell industry has developed more durable membrane electrode assembly (MEA) to avoid failures and extend the operating lifetime, but PEM fuel cells remain vulnerable to hydrogen leaks which can lead to performance degradation and potential safety issues. While the onset of membrane degradation can be delayed, the initiation of MEA pinholes is inevitable with existing technology measures.
Due to the existence of pinholes in the MEA, hydrogen may leak through the MEA from the anode to the cathode. At sufficient rates of hydrogen cross-over leak, the fuel cell performance drops due to the direct recombination with reactant oxygen on the cathode side. This recombination affects the available amount of oxygen used for the electrochemical reaction. In severe cases, the fuel cell might suffer fuel and/or air starvation. Direct recombination of fuel with oxygen results in the formation of water on the cathode side, leading to air starvation of the affected cell because of the consumption of oxygen and/or water accumulation in the cathode.
Prior work dealing with MEA pinholes is limited. Weber (Adam Z. Weber, “Gas-Crossover and Membrane-Pinhole Effects in Polymer-Electrolyte Fuel Cells”, Journal of Electrochemical Society, 155 (6) B521-B531, 2008) developed a mathematical model to simulate the effect of pinholes in a PEM fuel cell. He showed the performance drop in terms of cell voltage and current density. The drop in current density was also considered by Lin et al. (R. Lin, E. Gülzow, M. Schulze and K. A. Friedrich, “Investigation of Membrane Pinhole Effects in Polymer Electrolyte Fuel Cells by Locally Resolved Current Density”, Journal of The Electrochemical Society, 158 (1) B11-B17, 2011). Hydrogen leak can also be detected by the increase of leak current and drop in voltage (Soshin Nakamura, Eiichi Kashiwa, Hidetoshi Sasou, Suguru Hariyama, Tsutomu Aoki, Yasuji Ogami and Hisao Nishikawa, “Measurement of Leak Current Generation Distribution in PEFC and Its Application to Load Fluctuation Testing Under Low Humidification”, Electrical Engineering in Japan, Vol. 174, No. 1, 2011; B. T. Huang, Y. Chatillon, C. Bonnet, F. Lapicque, S. Leclerc, M. Hinaje, S. Rael, “Experimental investigation of pinhole effect on MEA/cell aging in PEMFC”, International journal of hydrogen energy 38: 543-550, 2013). However, detecting small hydrogen leaks by measuring the cell voltage is not feasible, where the degraded voltage is very minimal with the gradual increasing of leak rates.
These studies have also only dealt with a single small-sized MEA. In actual industrial applications, however, larger stacks containing multiple unit cells in series are used to provide large amounts of power; that is, on the order of tens of kilowatts. Because of the large size and a lack of appropriate models, a stack of this size requires a diagnostic tool that is able to detect hydrogen leak in operation and quantify its rate effectively. Knowing the amount of hydrogen leak during fuel cell operation may facilitate the establishment of mitigation criteria to reduce its effect on stack performance.